1. Field of the Invention
The present invention relates to a method of producing a thin film magnetic head, and more particularly to a method of producing a thin film magnetic head by which strong intensity of magnetic field for writing data on a magnetic recording medium can be obtained without generating excessive ineffective leakage magnetic flux.
2. Prior Art
FIG. 1 shows the sectional construction of the known thin film magnetic head which may be used in a magnetic recording apparatus. In FIG. 1, 1 designates a substrate on which an insulation layer 2 made of material such as Al.sub.2 O.sub.3 is formed. In addition, a lower pole 3 made of soft magnetic materials is formed on the insulation layer 2 by the plating method, evaporation method or sputtering method. Then, an insulation layer 4 made of the material such as Al.sub.2 O.sub.3 is formed as the film on the lower pole 3. Next, an insulation layer 5 made of organic substance such as photoresist is formed, and a coil 6 made of conductive material is further formed. In addition, another insulation layer 7 made of the organic substance such as the photoresist is formed in such a manner that the coil 6 is buried within this insulation layer 7. Thereafter, similar to the lower pole 3, an upper pole 8 made of the soft magnetic materials is formed. Lastly, a protection film 9 made of the insulation material such as Al.sub.2 O.sub.3 is formed. The insulation layer 4 between the lower pole 3 and the upper pole 8 functions as a gap spacer, and the magnetic fluxes from an edge portion of these poles spaced with this gap spacer are used for writing data effectively.
In order to perform the recording with high bit density (e.g., the recording with the bit density of 2500 BPI (Bit Per Inch) or more) in the above-constructed thin film magnetic head, each film thickness of lower pole 3 and upper pole 8 must be set smaller than 1 .mu.m (i.e., 1 micro-meter). In this case, the film thickness of soft magnetic material of each pole must be thin, so that its magnetic resistance must be increased. Hence, each of the lower pole 3 and upper pole 8 is saturated magnetically. For this reason, there is a disadvantage in that writing efficiency within writing and reading efficiency (i.e., R/W efficiency) of the thin film magnetic head is especially lowered so that writing characteristic of the thin film magnetic head must be deteriorated.
On the other hand, another conventional thin film magnetic head having the sectional construction as shown in FIG. 2 is also proposed. In FIGS. 2, 10 and 11 respectively designate a lower pole and an upper pole each of which is made of the soft magnetic materials, and 12 designates a substrate. In this head, the film thicknesses of these poles 10 and 11 at a inner gap portion B and read gap portion C are set larger as compared to the film thicknesses of these poles at a front gap portion A. Due to such construction, the magnetic resistances of lower pole 10 and upper pole 11 are lowered so that magnetic saturation of these poles can be restrained.
However, the above-constructed thin film magnetic head must have the following disadvantages. More specifically, since this head employs the step construction in that the film thickness of lower pole 10 becomes thicker in the opposite side of the substrate 12 (i.e., in the side of upper pole 11), the formation of each film piled on the lower pole 10 in the subsequent process and the formation of photoresist pattern by which these films are patterned must become difficult due to the stage difference made by this step construction. For this reason, the productivity of thin film magnetic head is lowered in its production process. In this case, the stage difference for the upper pole 11 must be larger as compared to that for the upper pole 8 in the thin film magnetic head having the sectional construction as shown in FIG. 1. Therefore, there is another disadvantage in that the magnetic characteristic of upper pole 11 is deteriorated in the inclination portion between the front gap portion A and the inner gap portion B.
Further, in the writing and reading period in the thin film magnetic head having the sectional construction as shown in FIG. 2, most of the magnetic fluxes are leaked in vain via a step portion D and then such leaked magnetic fluxes which are effective for the writing are flown in the direction from the upper pole 11 to the lower pole 10 or its reverse direction. Hence, the magnetic fluxes are not effectively passed through the upper pole 11 or lower pole 10, so that the R/W efficiency must be lowered.
In order to eliminate the above-mentioned disadvantages, still another magnetic head having the sectional construction as shown in FIG. 3 is proposed. In this magnetic head as shown in FIG. 3, a recess is formed at an insulation layer 20 in advance, and a first soft magnetic material layer 21 is formed such that the recess is buried within this layer 21. Then, a second soft magnetic material layer 22 having the predetermined pole formation is formed. Hence, a pile of such first layer 21 and second layer 22 forms the lower pole. Moreover, this magnetic head employs the reverse step construction in which the film thickness of lower pole at the inner gap portion B and rear gap portion C becomes thicker in the substrate side. Due to such reverse step construction as shown in FIG. 3, the disadvantages of the thin film magnetic heads as shown in FIGS. 1 and 2 can be eliminated.
Meanwhile, the recess within the above-mentioned thin film magnetic head as shown in FIG. 3 is formed by each of the following three methods each of which suffers its disadvantage to the contrary.
First method is as described in Japanese Patent Publication Laid-Open No. 60-193114 which employs the mechanical process using a brade, for example. By this first method as shown in FIG. 4, a recess is formed at a substrate 30 by the brade of dicer, and a lower magnetic layer 31 is provided at this recess or in the vicinity of this recess. On this layer 31, a non-magnetic insulation layer 32 which works as a gap length is piled. Then, a conductive layer 33 which forms a coil portion, its insulation layer 34 and upper magnetic layer 35 are sequentially formed. In addition, a protection layer 36 for protecting the main portion of thin film is provided, and a protection plate 37 is adhered to this protection layer 36. Thus, the thin film magnetic head is formed by the first method.
This first method uses the mechanical processing means, so that it is difficult to control the depth of recesses by micrometer order precision. In addition, it is also difficult for the first method to obtain the smooth cutting face. For these reasons, there is a disadvantage in that the magnetic characteristic of lower layer core must be deteriorated.
Next, second method is as described in Japanese Patent Publication Laid-Open No. 62-229512 which employs the wet etching method. In this second method, as shown in FIG. 5(a), a SiO.sub.2 film 41 of about 10 micro-meters is formed on a substrate 40, and a resist 42 is subjected to the patterning in order to effect the etching for the recess. Then, the SiO.sub.2 film 41 is subjected to the wet etching by liquid of HF+HNO.sub.3 so that a recess 43 is formed as shown in FIG. 5(b).
According to this second method, the recess 43 has the reverse trapezoidal shape. However, due to the overflow of etching liquid, the side edge must be formed at the recess 43. For this reason, there is a disadvantage in that the smooth slopes of such trapezoid can not be obtained as shown in FIG. 5(b).
Next, third method employs the dry etching method. As shown in FIG. 6A, a resist 52 is subjected to the patterning on an insulation layer 51 formed on a substrate 50, and then the ion beam etching is performed by irradiating the ion beam thereon. Thus, a recess 53 is formed as shown in FIG. 6B.
In this case, the etching is applied to the resist 52 and insulation layer 51 simultaneously. Therefore, the exposing surface of insulation layer which is not covered by the resist 52 is directly subjected to the vertical etching so that the recess 53 is formed. For this reason, the recess 53 must have the sharp wall face as shown in FIG. 6B. Thereafter, as shown in FIG. 6C, a first soft magnetic material layer 54 is buried in the recess 53, and then a second soft magnetic material layer 55 is provided on the first layer 54 so that the the thin film magnetic head is formed in accordance with the third method. In such construction, the magnetic fluxes are passed through the lower pole constituted by the first layer 54 and second layer 55 and then the magnetic fluxes are sharp gathered at a narrow portion A, wherein the magnetic fluxes are saturated. Hence, the magnetic fluxes are diverged via portions B and D which are positioned in the vicinity of the narrow portion A. As a result, the density of magnetic fluxes which must be converged at a portion E must be thin as compared to the density of magnetic fluxes at the narrow portion A. Therefore, the restriction effect (or gathering effect) of magnetic fluxes can not be obtained. In addition, the magnetic fluxes which are leaked from the portions B and D and then broadly spread forms the leakage magnetic field which is applied to the medium surface so that the magnetic field for writing must be broadened. For this reason, recording density of the medium will not be increased.